This invention relates generally to delay circuits and more particularly, it relates to a delay circuit utilized in conjunction with an electrically-operated device such as a gas solenoid valve for controlling the operation thereof. The delay circuit of this invention has particular application in industrial plants, manufacturing facilities, restaurants or any other facilities in which gas is utilized for operation of equipment.
Generally, it is known that in the operation of gas operated equipment such as burners, gas ovens and similar types of apparatus, an electrically-operated solenoid valve is frequently utilized for controlling the flow of gas in a main gas line to utilization points. If a plurality of gas-operated equipment is used, they commonly are coupled in series to the main gas line. One common problem encountered in the use of electrically-operated gas valves is that electrically power interruptions, even of the shortest interval, tend to interfere with the safe and convenient operation of the equipment. In such cases of a power failure such as a complete power loss or even a transient in the line voltage which only effects a momentary loss or drop in power, the electrically-operated solenoid valve connected conventionally upstream of the utilization points is caused to close and thus prevents further flow of gas to the individual burners or ovens. After closing of the valve, safety codes generally require that the gas line valve be manually reset. However, the requirement of manual reset for voltage fluctuations of short duration serves no practical purpose from a safety standpoint or otherwise. Complete or temporary power loss may be due to many circumstances such as disturbances on the line from the generating power source being overloaded, overloading by excess number of equipments being placed on the line internally, lightening, or fire and the like.
Regardless of the cause of the power interruption or fluctuation, the solenoid valve in a conventional control system will automatically close unitl a manually-operated reset switch or control device is activated. In many prior art control systems, the gas solenoid valve is closed and no indication of its interruption is known until an individual recognizes that no gas is being supplied to a utilization point. Often the interruption of the operation of the gas equipment may not be noticed for a considerable time after actual closing of the valve. This delay may cause disasterous effects on the cooking operation or other functions being performed by various equipment coupled to the main gas line causing delay, economic loss, and the creation of unsafe conditions. In order to restore the equipment back to normal operation after the power failure, it is necessary for an operator to reactivate each of the devices such as re-lighting each of the pilot lights of the burners and the like.
It should be apparent that it is extremely undesirable to require personnel to go through the laborous and time-consuming process of reactivating the equipment each time there is a mere transient in the line in which a momentary loss or drop in power is encountered in addition to the inherent disadvantages occurring because of the interruption of the operation of the equipment. It is, therefore, desirable to provide a delay circuit for automatically preventing the permanent closing or shutting of the gas solenoid valve when the power loss or fluctuation does not exceed a pre-determined time limit. In addition, it is advantageous to provide a device which will immediately and effectively warn operating personnel that the gas solenoid has been closed due to power interruptions greater than a predetermined interval.